1. Field of the Invention
The present invention relates generally to the field of semiconductor processing, and more specifically, to supporting, positioning or rotating a substrate during semiconductor device fabrication in a processing chamber.
2. Background of the Related Art
Integrated circuits have evolved into complex devices that can include millions of transistors, capacitors and resistors on a single chip. The evolution of chip design continually requires faster circuitry and greater circuit density that demand increasingly precise fabrication processes. One fabrication process frequently used is ion implantation.
Ion implantation is particularly important in forming transistor structures on semiconductors and may be used many times during chip fabrication. During ion implantation, silicon substrates are bombarded by a beam of electrically charged ions, commonly called dopants. Implantation changes the properties of the material in which the dopants are implanted to achieve a particular level of electrical performance. Dopant concentration is determined by controlling the number of ions in a beam of energy projected on the substrate and the number of times the substrate passes through the beam. The energy level of the beam typically determines the depth at which the dopants are placed. These dopants are accelerated to an energy level that will permit the dopants to penetrate or implant into the film at a desired depth.
During ion implantation, the implanted film often develops a high level of internal stress. In order to relieve the stress and further control the resulting properties of the implanted film, the film is typically subjected to a thermal process, such as annealing. Post-ion implantation annealing is typically performed in a rapid thermal processing (RTP) chamber that subjects the substrate to a very brief, yet highly controlled thermal cycle that can heat the substrate from room temperature to over 1000° C. in less than 10 seconds. RTP relieves the stress induced during implantation and can be used to further modify film properties such as changing the electrical characteristics of the film.
Generally, an RTP chamber includes a radiant heat source or lamp, a chamber body and a substrate support ring. The lamp is typically mounted to a top surface of the chamber body so that the radiant energy generated by the lamp impinges upon the substrate supported by the support ring within the chamber body. A quartz window is typically disposed in the top surface of the chamber body to facilitate the transfer of energy between the lamp and the substrate. The support ring is typically comprised of silicon carbide and extends from a bottom of the chamber body to support the substrate by its outer edge. An external motor is used to rotate the substrate and the support ring to compensate for variations in the radiant energy generated by the lamp impinging across the substrate surface that could heat the substrate non-uniformly. Typically, the RTP process is performed at a reduced pressure to minimize potential particle and chemical contamination of the substrate.
While RTP processes can heat and cool a substrate quickly, RTP processes often heat the entire thickness of the substrate. Uneven heating across the surface of the substrate can be a problem that is often experienced with RTP or other conventional substrate heating processes. For example, temperature variation often occurs in the area where the support ring contacts the outer edge of the substrate. Variation of substrate temperatures also may occur because the radiant heat source is applied to the top surface of the substrate which may include different device materials at various sections of the surface. The different device materials may have wide ranges of emissivities resulting in varying temperatures. Also, the bearing which is used to support and rotate the substrate and assembly is a potential source of substrate contamination and particle generation.
Therefore, is a need for an improved system adapted to support, position, or rotate a substrate during an annealing process which does not require direct contact with the substrate.